1. Field of the Invention
The invention relates to the continuous casting of a filament within a zone of effective vacuum. More particularly, the invention relates to an apparatus and method for continuously casting a glassy metal filament in a vacuum and continuously transporting the filament to an ambient atmosphere.
2. Description of the Prior Art
In the production of a glassy alloy continuous filament, an appropriate molten alloy is typically quenched at extremely rapid quench rates, usually at least about 10.sup.4 .degree. C. per second, by extruding the molten alloy from a pressurized reservoir through an extrusion nozzle onto a high speed quench surface, as is representatively shown in U.S. Pat. No. 4,142,571 for "Continuous Casting Method for Metallic Strips" issued March 6, 1979 to M. Narasimhan. U.S. Pat. No. 4,077,462 for "Chill Roll Casting of Continuous Filament" issued March 7, 1978 to Bedell, et al. shows a representative apparatus for casting metal filament on the peripheral surface of an annular chill roll. The apparatus has an arcuate, stationary housing disposed about the peripheral surface of the chill roll to delimit a gap between the chill roll peripheral surface and the housing interior, and has a means for providing a fluid stream into the gap.
Vacuum casting is ordinarily accomplished by locating a casting operation in an evacuated vacuum chamber, as representatively shown in U.S. Pat. No. 4,154,283 for "Production of Improved Metal Alloy Filaments" issued May 15, 1979 to R. Ray, et al. Then, after casting the filament, the chamber is opened to remove the filament. Such procedure is particularly tedious and inefficient because it in necessary to stop the casting operation,, break the seal of the vacuum chamber to remove the filament and then reseal and restart the casting operation. Because of the very high casting speeds, the cast filament accumulates very rapidly, often piling onto the casting chamber floor and requiring frequent interruption of the casting operation to remove the filament. A winder mechanism may be located in the evacuated chamber, but this would involve pumping down a chamber large enough to contain the winder device as well as the casting equipment.
U.S. Pat. No. 3,888,300 for "Apparatus for the Continuous Casting of Metals and the Like under Vacuum" issued June 10, 1975 to C. Guichard, et al. shows a device for casting a metal ingot in a vacuum. The device includes a dynamic airlock comprised of several suction chambers and includes rollers which support and center the ingot in the suction chambers as it moves therethrough. U.S. Pat. No. 2,367,174 for "Seal for Gas Pickling Furnace Muffles" issued Jan. 9, 1945 to R. F. Renkin shows a sealing structure comprised of a housing which contains pairs of sealing rollers. U.S. Pat. No. 3,032,890 for "Sealing Structures for Treating Chambers" issued May 8, 1962 to R. M. Brick, et al. shows a sealing structure comprised of a housing having pairs of rollers located therein, and means for exhausting any gases that leak into the areas between roller pairs.
When vacuum casting filaments at high speeds, however, the filament does not reliably exit the evacuated casting chamber without experiencing entanglements and choking of material in the exit sealing structure. In addition, the quench surface can become sensitized, causing the cast filament to adhere or "weld" onto the surface instead of breaking away as ordinarily occurs when casting in an atmosphere. This not only disrupts the casting operation but can also damage the casting equipment. As a result, conventional casting apparatus do not satisfactorily vacuum cast continuous filaments at high speed.